1. Field of the Invention
The present invention relates to an active sound effect generating apparatus for generating a sound effect based on the rotational frequency of an engine on a mobile body such as a vehicle or the like.
2. Description of the Related Art
Heretofore, there have been proposed active sound effect generating apparatus (also referred to as “ASC (Active Sound Control) apparatus”) for detecting an action made by the driver of a vehicle to accelerate or decelerate the vehicle and generating a sound effect based on the detected level of acceleration or deceleration in the vehicle cabin through a speaker in the vehicle cabin (see Japanese Laid-Open Patent Publication No. 54-008027 and U.S. Patent Application Publication No. 2006/0215846).
According to the proposed ASC apparatus, when the engine rotational speed increases based on an accelerating action, the speaker generates a sound effect having a high frequency and a large sound volume depending on the increase in the engine rotational speed, producing an enhanced staged sound atmosphere in the vehicle cabin.
According to U.S. Patent Application Publication No. 2006/0215846, a preferred sound effect is generated by changing the sound pressure level (gain) depending on a change (Hz/second) in the engine rotational frequency per unit time (hereinafter referred to as “rotational frequency change”) (see FIG. 14 of U.S. Patent Application Publication No. 2006/0215846).
The ASC apparatus disclosed in U.S. Patent Application Publication No. 2006/0215846, which changes the sound pressure level depending on the rotational frequency change, may generate an actual sound effect whose sound pressure level is not commensurate with the driver's action on the accelerator pedal, making the driver feel odd about the sound effect. For example, while the vehicle is running uphill, even if the driver presses the accelerator pedal strongly, the rotational frequency does not change greatly because of the increased hill-climbing resistance, and hence the sound pressure level does not increase commensurate with the increase in the depression of the accelerator pedal. Conversely, while the vehicle is running downhill, since the hill-climbing resistance drops, a large sound effect is generated even if the driver presses the accelerator pedal lightly. The above response that does not commensurate with the driver's action may possibly be caused when the vehicle runs not only on slopes but also on different types of roads and under different road conditions.